Electric arc furnace (EAF) dust is the dust collected from an electric arc furnace for melting scrap in a steel making process. EAF dust is classified as a hazardous waste by the Environmental Protection Agency and is designated the identification K061. EAF dust has a large heavy metals content, particularly lead, which is the main reason why it is classified as a hazardous material.
Tables I and II below show chemical analysis of EAF dust produced over a four month period during the manufacture of carbon steel (Table 1) and stainless steel (Table 2).
TABLE I ______________________________________ Carbon Steel Total (%) Jan. Feb. Mar. Apr. ______________________________________ C 20.0 20.0 20.0 20.0 Ca 19.60 21.00 24.50 23.10 Fe 28.8 25.50 17.10 17.40 Zn 16.40 14.30 9.85 11.90 Mn 2.20 2.05 2.25 2.15 Pb 2.55 1.70 1.48 1.21 Na 0.76 0.67 0.91 0.63 Si 0.13 0.33 0.29 0.31 Al 0.41 0.39 0.37 0.26 Mg 0.75 0.55 0.48 1.05 Cr 0.17 0.25 0.33 0.42 Cu 0.21 0.12 0.12 0.09 Ni 0.13 0.08 0.12 0.02 Cd 0.04 0.02 0.02 0.02 Mo 0.02 0.02 0.06 0.05 K 1.50 1.00 1.35 1.07 ______________________________________
TABLE II ______________________________________ Stainless Steel Total (%) Jan. Feb. Mar. Apr ______________________________________ C 20.0 20.0 20.0 20.0 Ca 2.50 25.2 16.0 13.0 Fe 30.0 26.1 21.6 24.3 Zn 8.10 10.5 5.60 5.35 Mn 1.90 1.95 1.75 1.65 Pb 0.90 1.10 1.01 0.71 Na 0.48 0.53 0.72 0.44 Si 0.06 0.38 0.30 0.26 Al 0.28 0.40 0.45 0.23 Mg 0.85 0.48 0.62 0.88 Cr 2.27 0.30 1.90 1.90 Cu 0.16 0.10 0.11 0.09 Ni 0.11 0.07 0.10 0.04 Cd 0.02 0.02 0.01 0.01 Mo 0.45 0.02 0.04 0.06 K 1.10 0.90 0.95 0.60 ______________________________________
Tables III and IV show parts by weight of different components found in the leachate of the same carbon steel samples shown in Table I and the leachate of the same stainless steel samples shown in Table II. In Tables III and IV, hexavalent chrome is identified as Cr(6).
TABLE III ______________________________________ Carbon-Leachate (mg/l) Total Jan. Feb. Mar. Apr. ______________________________________ Cr(6) 0.01 0.41 1.48 0.44 Cr 0.22 0.46 1.67 0.45 Pb 145.00 110.00 39.00 76.80 Cd 0.02 0.02 0.02 0.02 Ag 0.04 0.04 0.05 0.06 Ba 2.50 1.60 2.40 1.10 Hg 0.0022 0.0054 0.0011 0.0046 ______________________________________
TABLE IV ______________________________________ Stainless-Leachate (mg/l) Total Jan. Feb. Mar. Apr. ______________________________________ Cr(6) 4.30 0.68 2.63 6.30 Cr 6.40 0.83 2.63 6.62 Pb 0.26 60.5 64.0 37.2 Cd 1.93 0.02 0.02 0.02 Ag 0.04 0.06 0.05 0.06 Ba 1.2 1.40 1.0 1.0 Hg 0.0019 0.0047 0.0010 0.0005 ______________________________________
Tables III and IV indicate that a significant amount of lead and other metals in the dust are prone to leaching out. For this reason, EAF dust cannot be buried in the ground for disposal. Instead, some current methods require combining the dust with a heavy steel material to form a waste product which will not leach. Discarding EAF dust in this manner is an expensive process. EAF dust further poses a health risk due to heavy metal pollution by airborne fumes.
In a typical steel manufacturing process, EAF dust is produced in amounts of between about 0.7 and 1.6% based upon the total amount of steel produced. A need exists for a method of discarding heavy metal dust which method is both inexpensive and safe.
Japanese Publication No. 53-127511 discloses a method of using EAF dust in the production of bricks. The dust is mixed with a brick raw material, formed into bricks, and fired thereby incorporating the hazardous dust into the bricks. According to the Japanese publication, volatilized and recondensed metals produced during the brick firing process are collected in a baghouse on the kiln exhaust.
According to the Japanese publication, raw EAF dust is added in quantities from 30 to 50 weight percent to a normal clay brick mix, and fired in a tunnel kiln at between 630.degree. and 830.degree. C. in a normal manner. Volatilized and recondensed heavy metals are collected in a baghouse on the kiln exhaust. In a reproduction of the process taught in the Japanese publication, EAF dust was added in an amount of 40% by weight to a normal brick body and fired in a similar manner to that described. The resultant bricks were very friable and exhibited compressive strengths which averaged only 690 psi. Table V shows the results of the compressive strength test on five samples made according to the reproduction method. The bricks were tested flatwise. ASTM rated bricks in the United States are required to have a minimum allowable compressive strength of 1500 psi. Thus, a reproduction of the Japanese process failed to produce brick strong enough for U.S. standards. Further, it is expected that a significant amount of heavy metals may leach out of these weak bricks.
TABLE V __________________________________________________________________________ 40% BY WEIGHT RAW EAF DUST 5 Hour 24 Hour Compressive Submersion Submersion Maximum Strength psi in Boiling Water in Cold Water Saturation Sample # (Gross Area) % absorption % absorption Coefficient __________________________________________________________________________ 1 710 29.9 23.3 0.78 2 780 29.5 22.8 0.78 3 620 30.2 23.7 0.79 4 630 30.1 23.6 0.78 5 720 29.6 23.1 0.78 Average 690 29.9 23.3 0.78 __________________________________________________________________________
It is therefore desirable to provide a method of incorporating EAF dust into a raw brick material and producing a brick which exhibits a high compressive strength and no significant leaching of heavy metals.